Question

What is dead burnt plaster?

Answer 1

Plaster of Paris is obtained by heating gypsum. Following is the chemical equation for the reaction

CaSO₄.2H₂O → CaSO4.1/2H₂O + 11/2 H₂O

However, when heated beyond 393 K, all the water of crystallisation is lost resulting in the formation of anhydrous calcium sulphate. This anhydrous calcium sulphate obtained by the over-heating of gypsum is known as dead burnt plaster. It does not possess any properties of setting with water.